Why and How to sharpen squeegeesPrepared by FIMOR NORTH AMERICAWHY AND HOW TO SHARPEN SQUEEGEESCONTENTS:INTRODUCTION TO SHARPENINGTHE FUNCTION OF THE SQUEEGEEDUROMETERFREE-HEIGHTBLADE PROFILEBLADE EDGEWHY SHARPEN SQUEEGEEDOLLARS & SENSE OF SHARPENINGHOW TO SHARPENTHE SALES PITCHAPPENDIXINTRODUCTION TO SQUEEGEE SHARPENINGThere are plenty of benefits to properly maintaining production tools and equipment. A carpenter wouldn't last long with a dull saw blade. A machinist couldn't drill too many holes with a worn drill bit. They know that sooner or later, an end product made with poor tools will be unacceptable to the customer. They also know that dull and worn tools will slow production, often as much as 50%. Ultimately, they must consider their production costs. Is it more cost effective to refurbish such tools, or to replace them altogether?The squeegee is one of the most important tools used in screen printing. Unfortunately, it is also one of the most neglected. It is important because it controls the ink deposit and affects the color and sharpness of the printed image. However, most screen printers produce tens of thousands of impressions without evei bothering to evaluate the squeegee because it "seems to work," no matter what shape it's in. Unless the blade has an obvious flaw (like a "nick" that leaves a streak in the image), production seems to go on forever. When streaks or other problems do occur, the blade simply gets replaced and production continues.There are two things wrong with this picture of the squeegee:1.Just because a squeegee prints with no major visual flaws, doesn't mean that the image has not changed between the first and last impression (print). This quality difference may be acceptable to the printer, but not to a customer looking for uniformity from print to print. Furthermore, some image flaws (often mistaken as symptoms of mechanical problems) may actually be related to the squeegee blade and not the printing equipment.2.Replacing a squeegee blade is anywhere from 5 to 50 times more expensive (not to mention environmentally wasteful) than repairing (sharpening) it. Throwing away a squeegee after 50,000 impressions is like throwing away a drill bit after drilling only 50 holes - It's not very cost effective.THE FUNCION OF THE SQUEEGEEAlthough it looks simple, the squeegee is a highly complicated part of the printing process. Unlike the ink-related press parts in other printing processes (doctor blades, ink rollers, pressure rollers, pads etc.), the squeegee alone must perform the following functions:forcing the ink into the screen mesh (Figure 1A, page 2)keeping the mesh in contact with the substrate (Figure 2a, page 2)adapting the mesh to the shape of the substrate (Figu*s 2B, page 2)removing the excess ink from the screen mesh (Figure 1B, page 2)The squeegee must do each of these jobs well to make a good print. Yet, every time the squeegee's shape and size vary, it affects all four of these printing functions. Figure 3 provides a diagram of the standard squeegee. While all the components are important, we need only consider four main features.^urometerThis is a measure of the hardness/softness of the blade, which is usually made of polyurethane. The durometer, together with the physical size and shape of the blade determines its bending, flexing, and compression charactertstics. Durometer has a numerical value of compression ranging from 55 to 90, as provided by a Shore A testing gauge. A blade with a value of 55-65 is considered soft, 66-75 is medium, and over 75 is called a hard durometer.A hard-durometer blade fulfills three of the four printing functions better than a soft-durometer blade. Hard-durometer blades are also better at withstanding wear during printing. The only real advantage to a soft-durometer blade is that it can adapt the screen mesh to the substrate surface, a quality that is important when printing rough surfaces.Free- heightThis is the part of the blade that protrudes from the squeegee holder. It is an important dimension because it determines how much the blade will bend under pressure, This bending is proportional to the third power of the free height, for example, twice the dimension will result in 23=8 times more bending (Figure 4).When a squeegee blade bends, two things happen. First the angle between the blade and screen changes and, second, the amount of printing force transmitted to the substrate is reduced. You can think of the blade as a series of springs. When they are aligned with a force they transmitall the force. When the force is at an angle, the spring starts to bend and transmits less and less force (Figure 5). At a certain point, when the printing angle is reduced and insufficient printing pressure is applied, the squeegee can't work properly. It will adapt to the substrate poorly and it will remove less ink from the screen. The end result will be a thicker ink deposit. At this point most printers start to apply more pressure to the squeegee which will result in even more bending and totally unpredictable ink-deposit thickness.Blade profileThis is the shape of the squeegee blade as shown in Figure 6. Although the most frequently used shape is a simple rectangle, other shapes are also used for certain printing conditions. For example, a hard-durometer squeegee usually performs better than a soft one, but it has poor adaptability to the surface. By using a beveled blade, the printing edge becomes more flexible (similar to a soft durometer), while the rest of the squeegee retains its original stiffness.The three basic profiles available to printers are the rectangle (or straight edge), various beveled shapes, and the round (bull-nose) shape. The rectangular shape provides medium adaptability, maximum printing pressure, and a printing angle that is close to the angle setting of the holder. The beveled shapes provide maximum adaptability, reduced printing pressure, and a printing angle that is less than the set angle. The round profile provides the least adaptability of all profiles, minimum printing pressure, and a printing angle that is independent of the angle setting on press (it is always at a minimum). For these reasons, it deposits the most ink. A chart explaining the selection of various profiles and durometers is shown in Table I, page 4.Blade edgeThis feature is the "working end of the blade and it is the part that actually fulfills all four functions of the squeegee. The sharpness of this edge is the primary control of ink-deposit. A sharp edge will provide the minimum amount of ink and the maximum image definition. As the edge dulls and rounds, the ink deposit will increase. Eventually, this increase will adversely affect both color and image definition.When printing large, simple designs with opaque inks, this change in color and image definition may not be visually apparent. However, when printing fine-lines, four-color process, or when using semi-opaque (UV) and transparent inks, you will quickly see the deterioration of the squeegee edge. Just compare the first and last prints of a long run where the squeegee was not sharpened during production.SQUEEGEE SHAPEFORCE, MESH-OPENING, *Vf * VISCOSITY ^ Y*OFF-CONTACTSCREEN TENSIONADAPTATION TO>\ SUBSTRATE SURFACEINK-LAYER THICKNESS, IMAGE L EFiNiTIONSOFi DUROMETER|Medium force, use with large mesh openings and low viscosity inksf use with low tension screens or screens with minimum off-contactUse on rough or uneven surfaces, dented press beds and poorly set up presses \ Medio c e i hickness control and image definition \\NIMedium force, use wth large mesh op enngs and low viscosity inksUse with low tension sci eens or screens with minimum off-contactUse on rough or uneven surfaces, dented press beds and po;rly set up presses *Pooi thickness control an d image definition ; use for coating applicationsfMedium force, i se Vith large mesh openings and low viscosity inksUse wit! low tension sdeens or screens with minimum off-contactUse on uneven contoured surfaces (containers, etc.)Mediocre thickness contol and image definitionMedium force, use with large m esh openings and medium to low viscosity inks /"\\ \Use witi low tension sc et ns or screens with minimum off-contactUse on rough or uneven surfaces soft absor 'en' materials, win pressesPoor thickness cont on i nd image definition ; use for cot ting applicationsMEDIUM DUROMETER Q1High punlng fcrce, useful for a wide range of _ W \) meshesand ink viscositiesUse with high or low tension screens with appropriate off-contact distanceModerate adaptation : use \ J on even surfaces vith minimum textureGood thickness confol and image d efinition on well-set-up equipmentlHigh prin.ing force, useful foi a wide range ofmeshes and ink viscositiesUs e with high or low tension screens with appropriate off-contactdistance \VftVK^*W\0* r\XDesigned to accomodate a range of squeegee handle configurations, the Maxi is ideal for garment, graphic, container, or electronics printers using automatic presses. The sturdy design holds up to a 38" (97 cm) squeegee by the blade while the operator moves the wheel in fixed tracks across the squeegee. Two diamond wheels (60 and 120 grit) are included.serilor Maxitronic:This fully-automated version of the serilorMaxi will accomodate squeegees up to 37" (94cm) and controls all variables for optimum accuracy. The operator simply presets the number of cycles and the diamond wheel will automatically advance to remove .002"-.004" (2.-4 mils) of material per cycle. Unit includes a stand and vacuum system and two diamond wheels (60 and 120 grit).48" serilor Maxitronic:Recommended for larger textile and graphics printers, this slightly longer version of the Maxitronic includes all the features of the original, but sharpens squeegees up to 48' (122cm) long. This unit is built on a stand and includes a vacuum system and two diamond wheels (60 and 120 grit).serilor Kut:The Kut offers precision sharpening with two models for squeegees up to 60" or 76" (153 or 193cm) long. The unit's sturdy design holds the squeegee by the blade and even compensates for potential bending or bowing of long blades. Two diamond wheels (100 and 360 grit) are included.serilor Kutronic:A fully-automated sharpener with four models for squeegees up to 60''(153cm), 76"(193cm) 96" (244cm) or 120" (305cm) long. Offers the same quality features o: the Kut and controls all variables for optimum accuracy. Two diamond wheels (100 and 360 grit) are included.APPENDIX B: OUR SHAPED WHEELSAll sharpeners include two (2) straight edge mond wheels: Small machines include 60 and 120 grit while Kut and Kutronics maudi 100 and 360 grit. A.l wheels shown are offered as optional accessories. ^ YSquare-Edge Wheel (small and large wheels available):Diameter: small whe ;l 1", large wheel 6"Grits available- small wheels: 60; 120; 230; 360, f \large wheels: 100, 360 ^* W\0* Primary use: sharpening and polishing staight-edge ^* (square) squeegee blades.Center-Sharp Wheel (small wheel only): Major Diameter: '.480"Includei Angle: 60 v V * ^VT^ Grits available: 220 and 360Primary Use: Be vhng 3/16" squeegee blades to improve adaptation to rough or uneven substrates.Center-Bevel Wheel (small wheel only): Major diameter: 1.540" Included angle: 90or 70 Grits Available: 220Primary Use: Beveling Standard 3/8" squeegee blades to improve adaptation to rough or uneven substrates.Round Wheel (small wheel only)'Major Diameter: 1.500" ^VC^Radius of Curvature1 0.220"Grits available: 120Primary use: Rounding standard 318" squeege blades for heavier ink deposit.Round/Sharp Combo Wheel (small wheel only): Major Diameter: 1.5l0"Radius of Curvature: 0.125" V\V ^VfC^1 Grits Available: 120Primary use: For applications requiring variable ink-deposit thickness (e.g., garment printing). One edge of the squeegee remains square, the opposite edge has a 118" radius curve for heavier ink deposit.Hollow-Grind Wheel (small ud large wheels):Small wheel Major Diameter : 1.500"Large wheel Major Diameter: 6.000"lncluded angle: 160 ^*VC*